Aptamers are short oligonucleotide sequences that can specifically bind to a wide range of target molecules, such as drugs, proteins, and other inorganic or organic molecules with high affinity and specificity (Tuerk C, Gold L. Systematic evolution of ligands by exponential enrichment: RNA ligands to bacteriophage T4 DNA polymerase. Science (1990) 249: 505-510; Ellington, A D, Szostak, J W. In vitro selection of RNA molecules that bind specific ligands. Nature (1990) 346: 818-822). Aptamer binding is based on the ability of small oligonucleotides (typically 40-100 mers) to fold into unique three-dimensional structures that can interact with a specific binding region of the target molecule. Aptamers have inherent advantages that merit application as therapeutic agents (Hnatowich D J, Nakamura K. The influence of chemical structure of DNA and other oligomer radiopharmaceuticals on tumor delivery. Curr. Opin. Mol. Ther. (2006) 8(2): 136-143): 1) the ability to withstand high heat and denaturants, 2) rapid chemical synthesis, 3) small size (10-20,000 daltons vs 150,000 daltons for antibodies), and 4) non-immunogenicity (Jayasena S D. Aptamers: an emerging class of molecules that rival antibodies in diagnostics. Clin. Chem. (1999) 45: 1628-1650). Typical monovalent aptamers are potentially limited by reduced retention times on the target cell and lack of crosslinking and subsequent activation of targets. Aptamer-based bivalent ligands, however, have been demonstrated to increase affinity and function compared to the monovalent versions; for example, bivalent aptamers were used to activate thrombin and T cells (Kim Y, Cao Z, Tan W. Molecular assembly for high-performance bivalent nucleic acid inhibitor. Proc. Natl. Acad. Sci. USA. (2008) 105(15): 5664-5669; McNamara J O, Kolonias D, Pastor F, Mittler R S, Chen L, Giangrande P H, Sullenger B, Gilboa E. Multivalent 4-1BB binding aptamers costimulate CD8+ T cells and inhibit tumor growth in mice. Clin. Investi. (2008) 118: 376-386; Dollins C M, Nair S, Boczkowski D, Lee J, Layzer J M, Gilboa E, Sullenger B A. Assembling OX40 aptamers on a molecular scaffold to create a receptor-activating aptamer. Chem. Biol. (2008) 15(7): 675-682).
Recently, selection of a high affinity DNA aptamer (TD05) reactive with Burkitt's lymphoma was reported (Tang Z, Shangguan D, Wang K, Shi H, Sefah K, Mallikratchy P, Chen H W, Li Y, Tan W. Selection of aptamers for molecular recognition and characterization of cancer cells. Anal. Chem. (2007) 79: 4900-4907). At 4° C., TD05 binds to an epitope on B cell surface mIgM BCR, exclusively expressed on B cells and most B-cell lymphomas (Mallikaratchy P, Tang Z, Meng L, Shangguan D, Kwame S, Tan W. Aptamer directly evolved from live cells recognizes membrane bound immunoglobin heavy mu chain in Burkitt's lymphoma cells. Mol. Cell. Proteomics (2007) 6: 2230-2238). Aptamer TD05 is not useful in vivo, however, because of its lack of affinity and stability at physiological temperatures in human plasma. Moreover, it was not evident that TD05 could reach target B cells in vivo for diagnostic and therapeutic applications if the epitope was also present on circulating IgM, which is found in the plasma at 450-1500 mg/L (Furst D E. Serum immunoglobulins and risk of infection: how low can you go? Semin. Arthritis Rheum. (2009) 39(1): 18-29). Although aptamers have the potential to be potent therapeutics for addressing a large number of conditions and diseases, such aptamers do not have characteristics that permit utility for administration to prevent or treat conditions or diseases, because of lack of persistence in circulation, susceptibility to nuclease attack, and poor affinity for the target molecule, among other disadvantages.
Aptamers with utility in vivo for treating cancers such as but not limited to B-cell lymphomas, as well as for the prevention or treatment of other conditions or diseases, are needed.